Many commercial emissive display devices generate visible light using electron beam or ultraviolet radiation incident upon a phosphor, such as in cathode ray tube (CRT) or AC plasma visual displays. A less well known display technology, typified in Bischel et al. U.S. Pat. No. 5,544,268, incorporated herein by reference, uses optical waveguides to convey light from a light source onto a display screen. Waveguide-based flat panel displays generally utilize planar and/or channel waveguides. They typically include several parallel channel waveguides to be formed on a substrate. Optical switches are located either in or on the channel waveguides at predetermined matrix locations across the display screen. Optical energy injected into the channel waveguides is extracted at these predetermined positions by the optical switches and directed toward pixel structures which may, in certain embodiments described in the '268 patent, include re-radiators to emit light from the pixel structure towards a viewer. Such reradiators can include out-of-plane reflectors, scattering materials, or luminescent materials which emit at a wavelength which may differ from the wavelength of the input optical energy. Metal reflectors on or near the visible light emitting pixels are used in a variety of ways in different display architectures to redirect visible light emitted by phosphors into a preferred direction to achieve enhanced brightness at the viewer location. For example, Thomas U.S. Pat. No. 5,097,175, incorporated herein by reference, describes a pixel structure for CRT displays, where a material that emits visible light upon excitation with an electron beam is deposited on a transparent substrate in the form of a parabolic shaped cell that is coated with a reflective metal layer to redirect visible light emitted inside the cell through the substrate toward a viewer.
In another example of the use of reflectors to direct light for a visual display, Murata U.S. Pat. No. 5,055,737, incorporated herein by reference, describes a luminescent screen which contains a material that emits visible light when excited by light incident from the viewing direction. This screen contains a reflective structure that redirects light from the emitting material, that otherwise would propagate in undesired directions, back toward the viewer, thereby enhancing brightness.
Thus the conventional function of reflectors used in displays is to direct the light generated in the pixel toward the viewer. Such reflectors do not serve to enhance the efficiency of conversion to visible light of pump energy such as that from an electron beam in a CRT or from the ultra-violet light in a plasma display. Optical performance, including the conversion efficiency, brightness, and chromaticity, of display pixels containing certain optically activated luminescent materials such as phosphors, glasses, or crystals would benefit from increasing the amount of absorbed pump radiation. Therefore a different kind of reflective pixel structure is needed which confines the pump radiation while allowing for the emission of generated light.